Foam insulation in existing walls - good idea?

pompeiiFebruary 12, 2008

We want to have our attic and walls insulated, and just had an estimate done by USA Insulation. They would insulate the attic by blowing in some white fluffy stuff (I think he called it encapsulated fiberglass) and fill the exterior walls with foam. He said it was low-expanding, so although it would fill the cavities, there wasn't any risk of wall damage from over-expanding foam. Our home was built in 1957 and has very little insulation. Our heating bills are through the roof (no pun intended), we heat with hot water baseboard heat and the boiler is only a few years old so it's not the problem.

Is foam in the walls a good idea? Once we do it, it's there forever, so I want to make sure it's the right choice. He quoted $4900 for our one story 2200 sf home, including the attic, walls and foundation. I'm not really asking if that is a good price; I really want to know if there are any drawbacks to the foam.

I'd like to make a decision fairly soon, so if anyone has experience with this type of insulation system, I'd love to hear about it.

Here in the UK most houses are brick, and since the 1920s most had cavity walls, but no insulation inside them. The cavity helps a lot, but adding insulation helps even more. It's a very popular home improvement.

There are various materials used, but plastic type foams are most common now. They usually have the highest insulation value and they don't settle or slump in the walls. In the past loose insulation was used, but it tended to compact over time and leak out of holes too. The advantage of loose is that it can be sucked out again, but the only reason I can think why you would want to do this is to replace it because of the inherent problems with loose insulation.

We had foam insulation put in the cavity walls of one house we lived in. It worked fine and we noticed a difference in the house. It felt warmer and heating bills were lower.

Also, have you checked if there are any grants available from the utility company or local government for insulation work. This type of thing is increasingly common in Europe, and perhaps some parts of the US?

bry84,
Thanks for the input. The only help we can get with the cost is a $500 credit back on our federal taxes and there is talk about another $300 rebate from the electric company. The rest would be out of pocket, except of course, that we would save it on heating/cooling bills.

I'm glad to hear that there aren't any known problems with this. That's really what I wanted to hear. I like the foam for the reasons you state: it fills the cavities and doesn't settle like blown in insulation would.

We got another bid last night for foaming the walls with Air Krete, which is a cement-based foam. He would also blow cellulose into the attic. His bid was $1500 higher than the poly foam, but supposedly it will not shrink or crack which the poly foam can do after a few years, and he will use cellulose instead of fiberglass in the attic, which we know is better. If we diy the attic but have him foam the walls, then we can do the entire house for about $4500.

We have decided to not go with the poly foam and blown in fiberglass. We have another guy coming Monday to give us a bid on dense pack cellulose in the walls. I expect him to be the least expensive, so I wonder how much better the air krete foam system is, to justify the extra cost? The cellulose guy's preliminary bid over the phone for walls and attic was about $4000.

They say the R per inch is 3.9, which is a touch better than dense pack cellulose at 3.7 -- probably not enough to make much difference.

A well done cellulose job will dense pack the cellulose in the wall cavity such that it fills very well and never settles. It can also be done poorly and leave voids and settle, so I'd try to learn as much as you can about how good the cellulose guy is.

One question I would have about the Air Krete is whether they ever have any problem with the wall drying out. It sounds like they put quite a bit of moisture in the wall.

Another think to think about is vapor barriers. If you have no vapor barrier in the wall now, I would think about using a vapor barrier paint on the walls, and also sealing up all the holes (e.g. outlets). The cellulose and (I would guess) the Air Krete are permeable to water vapor, and should handle some water vapor migration out the walls, but its good to be on the safe side.

Maybe you could let us know what the cellulose bid is?

Years ago a friend and I were thinking of starting an insulation business. We went out on a job with a couple guys who wanted to sell their business. This was the Ureaformaldehyde foam, which has since be discredited. Anyway, these guys intentionally sprayed in the wrong mix of the the resin and catylist because the catylist was cheaper -- so they did a bad job just to save themselves a few bucks. My point is, get a good contractor :)

I would wonder if the foam you are inserting into the walls, if it is ever burned does it produce Non-Toxic fumes?
Safety is my concern.

Fiberglass doesn't burn so even when placed between walls as insulation should a fire ever occur you don't have the problem of it spreading Cause I would venture that most of those British built construction doesn't have Fire-stops in them from floor to floor.

I'd have a check with the town's fire marshal before I stuck anything in the cavity; including cellulose.

We've decided on cellulose in both the walls and attic. We'll hire a contractor to dense pack it in the walls, but my husband and son are going to blow it in the attic. DS comes home for spring break in a week - this is how he'll be spending a couple of his days. But since we'll pay him part of the money we'll save over hiring it out, he should be happy.

gardeninprogress, what percentage do you figure it saved you on heating bills? Did you have any insulation before?

I remember reading somewhere that insulation in the floor of the attic is the big saver because heat rises, and insulating the walls is less crucial. The other thing is making sure you have really good windows, low E, double pane, and good doors. Make sure your weather stripping is in good shape. Are there drafts in your wall light switches and electrical outlets. Seal them up before you spend big bucks insulating the walls. I would give these areas attention first before insulating the walls.

Insulating the walls will cost $1800, which I don't really look at as big bucks. According to the calculator solargary linked to (thanks, solargary) we will save about $1100 in heating costs alone per year for just the attic, since we have no insulation in either the walls or attic now. It should cost about $750 to diy the insulation in the attic, so that should repay us right away. I'm not sure how many sf to calculate for the walls, but even if it takes 2 or 3 years to pay us back, it will be well worth it.

We do have the insulating pads behind all the outlets. The windows are another story, and we are working on how best to handle the heat loss through those. They are original (1957) Pella double pane casement windows, and I'm sure we could do better if we had the budget. Next winter, I plan to bubble wrap the bedroom windows at least.

Thanks for the suggestions, solargary. We have hot water baseboard heat, so no ductwork to worry about. I will forward your suggestion about the great stuff to my husband, so he can take care of any other openings.

Also if you have Columbia Gas service they have an excellent program for assistance on insulating and air sealing your house.

If you have not insulated your attic yet you should also
air seal it prior to insulation. As with all things the law of physics apply. Wet to dry, warm to cold.
If you have your walls and attic insulated without properly air sealing it will helpbut you will not get the total benefit. Use some great stuff and seal every crack in your attic, this includes the seams at the wall top plates where drywall meets them. Also foam all elctrical and light fixtures. Be sure to properly seal all duct work.
Be sure that all bath and kithen exhaust fans are properly ventilated and that soffitt vents are properly installed.

Cellulose is the best in all areas walls and attic.

Also if you have a basement or crawl space be sure to insulate the rim joist area with polystyrene board.
You must seal the complete envelope.

I see the advantages of the spray foam products, but besides the added cost, what are the potential problems say with moving electrical wiring or plumbing piping in the exterior walls for potential future work? Since none of the foam products can be DIY projects I assume a professional would need to come in to 'fix' even a small area that needed to be remodeled.